At 7.20pm on Saturday night Mo Farah will step out on to the Olympic track for third time in seven days. Surrounding him will be three Ethiopians, Yenew Alamirew, Hagos Gebrhiwet and Dejen Gebremeskel, who are all quicker over 5,000m. There will also be two Kenyans, Thomas Longosiwa and Isaiah Koech. They are quicker than him. too. The blunt truth is that Farah is only the 11th-fastest man over the distance this year, and has the seventh-quickest personal best of the 15 runners in the field. The odds are stacked against him.

If Farah can win a second gold, he will go down not just as the greatest distance runner in British history but as one of the best the world has ever seen. Only six men have ever won the 5,000m and 10,000m double at one Olympic Games, and each of them has a place in the annals of the sport, from Hannes Kolehmainen in 1912, to Emil Zatopek and Vladimir Kuts in the 1950s, on through Lasse Viren and Miruts Yifter in the 1970s and 80s. Since then only Farah's great rival Kenenisa Bekele has done it, in 2008. What really gives an idea of just how hard it is to do, though, is the list of great runners who tried and failed. It was too tough for both the Flying Finn Paavo Nurmi and Haile Gebrselassie.

It will come down to how much Farah wants to win. At the world championships in 2011 he did manage to win medals in both events, which, again, were only a week apart. But then he had finished second in the 10,000m and was desperately hungry to win a first world title in the shorter race.

That motivation undoubtedly spurred him on through the gruelling schedule. This time, Farah has already received the acclaim that comes with being an Olympic champion. That takes a toll in itself, physically and mentally. The extreme emotions Farah felt last Saturday still will not have settled. He had been preparing for that race for four years. He has had six days to get ready for this one, and that time has been taken up with the rounds of interviews and other fripperies that come with winning.

Farah's coach, Alberto Salazar, the genius behind every single step the athlete has taken in the past two years, reckons that the gold in the 10,000m will only "take the pressure off him". But in the heats on Wednesday, Farah looked like a tired man. He finished third, and his time of 13min 26sec was only the 15th-fastest of the round. More worrying, though, was the way in which Koech and Hayle Ibrahimov kicked past him in the final lap. Salazar has spent the past 12 months honing Farah's speed over the last 400m, correcting the error in the Briton's sprinting technique that cost him the 10,000m title at the worlds last year. This season, the fast finish has been his signature style.

The Ethiopians will try to set up Gebremeskel, to give the 22-year-old the best chance of winning. At the world championships in Daegu last year he took bronze behind Farah, but since then he has run the fifth-quickest time in history. Farah will try to team with his training partner Galen Rupp. Expect Rupp's USA team-mate, canny old Bernard Lagat,, at 37 the shrewdest man in the field, to shadow whoever is at the front as the race reaches the final stages, ready to pounce at the last lap.

Of course Farah will have 80,000 people roaring him on, an advantage that could outweigh all those reasons to bet against him. But he will need every single voice in the crowd to be at its loudest if he is going to do it.